Add a crate_type attribute

Author: sfackler

lib.rs

@@ -56,6 +56,7 @@ fn main() {
  */
 
 #[crate_id="github.com/sfackler/rust-postgres"];
+#[crate_type="lib"];
 #[doc(html_root_url="http://sfackler.github.io/rust-postgres/doc/")];
 
 #[warn(missing_doc)];